Posterior vitreous detachment (PVD) happens as a normal part of aging. The vitreous gel shrinks and separates from the retina. PVD normally happens over a period of time, and it's something that you won't feel.
It happens because the vitreous gel in the middle of your eye begins to change by the time you are 40 or 50. The gel's normal structure breaks down in a process called syneresis. Parts of the gel shrink and lose fluid. The fluid collects in pockets in the middle of the eye, and thick strands of the gel form and drift through the eye. These strands appear as floaters.
This kind of PVD usually does not cause any problems. But if the vitreous gel is strongly attached to the retina, the gel can pull so hard on the retina—a process called traction—that it tears the retina. The tear then allows fluid to collect under the retina and may lead to a retinal detachment.
In addition to normal, age-related changes in the vitreous gel, PVD can also result from eye injury or inflammation or can happen after eye surgery. This kind of PVD may occur suddenly and may also cause a retinal tear.
The main symptoms of PVD are floaters and flashes of light. Having floaters or flashes does not always mean that you are about to have a retinal detachment, but it is important to tell your doctor about these symptoms right away. A sudden change in these symptoms could be a warning sign of a retinal tear or detachment.